JPH06135135A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material imparting high printing recording density, having high gloss, excellent in preservability and also excel lent in the recording aptitude of a full-automatic labeller. CONSTITUTION:An undercoat layer based on pigment and 1 to 20wt.% of an aqueous binder, a thermal recording layer containing a color former and a coupler developing a color upon the contact with the color former, an intermediate layer containing an aqueous binder and an overcoat layer containing an ionizing radiation curable resin are successively provided on base paper to constitute a thermal recording material. This thermal recording material is irradiated with ionizing radiation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having high gloss, high recording density, excellent storage stability and excellent recording suitability.

[0002]

2. Description of the Related Art Conventionally, a heat-sensitive recording material which utilizes a color-forming agent and a color-forming reaction between the color-forming agent and a color-forming agent which develops a color by contacting both color-forming substances with heat to obtain a color-developed image. Is well known. Since this thermal recording material is relatively inexpensive, the recording equipment is compact, and its maintenance is relatively easy, it is used in a wide range of fields such as recording media for facsimiles and various computers, thermal labels and the like. . However, there are drawbacks such as poor fingerprint resistance and solvent resistance. For example, when human skin oils or solvents come into contact with the recording layer, the recording density is lowered, or unnecessary coloration called background fog occurs.

As a method for solving such a drawback, a method of coating an aqueous emulsion of a resin having film forming ability and chemical resistance on the heat-sensitive recording layer (JP-A-54-54).
No. 128347), a method of coating a water-soluble polymer compound such as polyvinyl alcohol (Shokai 56-125354), and the like. However, due to the improvement, new defects are accompanied, and satisfactory results have not been obtained.

For example, when an aqueous resin coating is applied on the heat-sensitive recording layer, it is necessary to limit the drying temperature in order to avoid color development of the recording layer due to high temperature drying, which inevitably results in insufficient curing of the resin layer. The phenomenon that the recording head and the resin layer adhere to each other during recording occurs. Therefore, a method of applying a resin component that is cured with an electron beam onto the heat-sensitive recording layer and curing the resin component with an electron beam is also proposed,
The storability of prints is not sufficient, and the resin layer which is cured by electron beam may cause adverse effects such as color development of the thermosensitive recording layer immediately after coating and fading of a recorded image.

As a result of studying the improvement of such defects, the present inventors provided an intermediate layer such as an aqueous resin on the thermosensitive recording layer, and provided an overcoat layer containing an electron beam curable resin thereon. It was found that a heat-sensitive recording material having improved recording storability without fogging of the recording layer and having a wide range of surface characteristics and excellent recording characteristics can be obtained. Filed as.

Further, a method of providing an undercoat layer between the substrate and the heat-sensitive recording layer in order to increase the sensitivity of the heat-sensitive recording material (Japanese Patent Laid-Open No. Sho 61-206).
No. 58-134788) has been proposed, but in recent new applications, satisfactory results have not been obtained with respect to recording characteristics and storage stability.

[0007]

In recent years, the use of heat-sensitive recording materials as product labels has been increasing, and in particular, the demand for heat-sensitive recording labels suitable for microwave ovens is increasing. At present, these labels have a low thermal recording sensitivity so as not to cause color fog even at high temperatures in a microwave oven.

However, more recently, high-speed recording is often performed by a full-auto labeler or the like, which causes a problem of insufficient thermal recording sensitivity. It is considered that the sensitivity can be improved by providing an undercoat layer between the base paper and the heat-sensitive recording layer, but the heat-sensitive recording material provided with the overcoat layer containing the ionizing radiation-curable resin has a high surface barrier property. Therefore, when printing a label, there may occur a problem called a printing blister in which the printing portion swells.
When general coated paper is used as the base paper, printing blisters easily occur due to the high barrier property of the coated paper.

As a result of earnest studies on such a problem, the present inventor has found that the problem can be solved by controlling the binder content in the undercoat layer, and completed the present invention.

[0010]

SUMMARY OF THE INVENTION The present invention comprises a base paper,
An undercoat layer containing a pigment and a content ratio of 1 to 20% by weight of an aqueous binder as a main component, a heat-sensitive recording layer containing a color-forming agent and a color-forming agent that develops a color when contacted with the color-forming agent, an intermediate layer containing an aqueous binder, A heat-sensitive recording material comprising an overcoat layer containing an ionizing radiation curable resin, which is successively provided and irradiated with ionizing radiation.

[0011]

In the present invention, examples of the pigment contained in the undercoat layer include calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, calcined kaolin, Examples thereof include clay, calcined clay, inorganic pigments such as colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea-formalin resin filler, and organic pigments such as raw starch granules. The amount used is 60 to 95% by weight, preferably 80 to 95% by weight, based on the total weight of the undercoat layer.
Among these pigments, calcium carbonate and calcined kaolin are particularly desirable.

As the aqueous binder used in the present invention,
There are water-soluble binders and water-dispersible binders, and the following substances are exemplified. As a water-soluble binder; fully saponified or partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol having an acetoacetyl group introduced by reacting polyvinyl alcohol with diketene, polyvinyl alcohol and fumaric acid, phthalic anhydride, trimellitic anhydride , A reaction product of a polycarboxylic acid such as itaconic anhydride or an esterification product of these reaction products, further vinyl acetate and maleic acid, fumaric acid,
Carboxy-modified polyvinyl alcohol obtained as a saponification product of a copolymer with an ethylenically unsaturated carboxylic acid such as itaconic acid, crotonic acid, acrylic acid and methacrylic acid, and olefin sulfone such as vinyl acetate and ethylene sulfonic acid, allyl sulfonic acid Sulfonic acid-modified polyvinyl alcohol obtained as a saponification product of a copolymer with an acid or a salt thereof, vinyl acetate and ethylene, propylene, isobutylene, α-octene, α-dotecene, α-
Olefin-modified polyvinyl alcohol obtained by saponifying a copolymer with olefins such as octadodecene, nitrile-modified polyvinyl alcohol obtained as a saponification product of a copolymer of vinyl acetate and acrylonitrile, nitriles such as methacrylonitrile, acetic acid Amide-modified polyvinyl alcohol obtained by saponifying a copolymer of vinyl and amides such as acrylamide and methacrylamide,
Pyrrolidone-modified polyvinyl alcohol obtained by saponifying a copolymer of vinyl acetate and N-vinylpyrrolidone,
Cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, caseins, acacia, starches such as oxidized starch, etherified starch, dialdehyde starch, esterified starch and the like.

As a water-dispersible binder: styrene-butadiene copolymer emulsion, vinyl acetate-vinyl chloride-ethylene copolymer emulsion, methacrylate-
Butadiene copolymer emulsion and the like.

In the present invention, among these water-soluble or water-dispersible binders, various polyvinyl alcohols, oxidized starches, and styrene-butadiene copolymer emulsions are particularly preferable. It is important that the amount used is in the range of 1 to 20% by weight based on the total weight of the undercoat layer. If it is less than 1% by weight, there is a problem in the film forming property of the layer, and if it is more than 20% by weight, printing blisters are likely to occur during printing of the thermal recording label. Further, from the viewpoint of storability, it is desirable to use within the range of 5 to 20% by weight.

The coating solution containing these substances is prepared by dispersing it in water as a dispersion medium by means of a mixing and stirring grinder such as a ball mill, attritor or sand mill.

Further, various auxiliaries can be added to this coating solution, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate-sodium salt,
Examples thereof include dispersants such as alginates and fatty acid metal salts, ultraviolet absorbers such as benzophenone-based and triazole-based, and other defoaming agents, fluorescent dyes, coloring dyes and the like. The coating amount of the coating liquid for undercoat layer is in the range of about ² to ²⁰ g / m ² , preferably about 3 to 15 g / m ^{2 as} a dry weight.

As the support, for example, high-quality paper, coated paper and the like are used, but in order to fully exert the effect of the undercoat layer, high-quality paper is preferably used, particularly as a thermal recording medium. Dedicated base paper with quality characteristics tailored to the application is desirable. The coating method of the recording layer can be formed by a well-known conventional technique, for example, a method of coating a coating solution by bar coating, air knife coating, rod blade coating, pure blade coating, short dwell coating, etc. and drying. . Of these, various blade coatings having a uniform coating surface are preferable.

Further, by further increasing the smoothness of the surface of the undercoat layer, a recording material having a high recording density and printing image quality can be obtained. Therefore, for example, it is smoothed by a super calender, a soft calender, a gloss calender or the like. It is desirable to adjust the Bekk smoothness of the surface of the undercoat layer to 50 seconds or more, more preferably 100 seconds or more.

In the present invention, a heat-sensitive recording layer is provided on these undercoat layers, but the combination of the color former and the color former contained in the heat-sensitive recording layer is not particularly limited, and both can be heated. Any combination that causes a color reaction upon contact can be used, for example, a combination of a colorless or light-colored basic dye and an inorganic or organic acidic substance, and a higher fatty acid metal salt such as ferric stearate. Examples thereof include combinations with phenols such as gallic acid.

In particular, when it is applied to a combination of a basic dye and an acidic substance, the recording characteristics are extremely excellent, which is preferable. Various types of basic dyes that are colorless or light-colored are known, and examples thereof include the following. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) phthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrole- 3-yl) -6-dimethylaminophthalide and other triallylmethane dyes,
4,4'-bis-dimethylaminobenzhydryl benzyl ether, N-halophenyl-leuco auramine, N
Diphenylmethane dyes such as -2,4,5-trichlorophenylleuco auramine, benzoyl leuco methylene blue, thiazine dyes such as p-nitrobenzoyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-
Spiro dyes such as dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o- Lactam dyes such as chloroanilino) lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3
Fluorane dyes such as diethylamino-7-chlorofluorane and 3-dibutylamino-7- (o-chlorophenylamino) fluorane. Other examples include the colorless or light-colored basic dyes described in JP-A-3-79387.

There are various types of inorganic or organic acidic substances as colorants that develop color by contacting with a basic colorless dye, for example, activated clay, acid clay, attapulgite, bentonite, colloidal silica, silicic acid. Inorganic acidic substances such as aluminum, 4-hydroxy-4′-isopropoxydiphenyl sulfone, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol,
In addition to β-naphthol, 4-hydroxyacetophenol, and the like, colorants described in JP-A-3-79387 can be mentioned.

In the present invention, the use ratio of the color former and the color former in the recording layer is appropriately selected according to the kinds of the color former and the color former used. For example, when a colorless or pale basic dye and an acidic substance are used, 1 to 50 parts by weight, preferably 1 to 10 parts by weight of the acidic substance is used per 1 part by weight of the basic dye. To prepare a coating liquid containing these substances, water is used as a dispersion medium, and a color-developing agent and a color-developing agent are dispersed together or separately by a mixing and stirring pulverizer such as a ball mill, an attritor, or a sand mill to prepare a coating liquid. Is prepared.

In this coating liquid, starch, hydroxyethyl cellulose, methyl cellulose,
Carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene
Maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, etc. are 10% of the total solid content. -40% by weight, preferably about 15-30% by weight.

Further, various auxiliary agents can be added to the coating liquid. For example, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, sodium salt,
Examples thereof include dispersants such as alginates and fatty acid metal salts, ultraviolet absorbers such as benzophenone-based and triazole-based, and other defoaming agents, fluorescent dyes, coloring dyes and the like.

If necessary, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, and particulate anhydrous. Inorganic pigments such as silica and activated clay, and sensitizers such as stearic acid amide, stearic acid methylenebisamide, oleic acid amide, palmitic acid amide, oleic oleic acid amide, and palm fatty acid amide are added.

Regarding the coating amount of the coating liquid for the thermal recording layer,
By dry weight 2~12g / m ^2, preferably from 3 to 10 g / m ²
A range of degrees is preferred.

In the heat-sensitive recording material of the present invention, an intermediate layer containing an aqueous binder is provided on the above-mentioned heat-sensitive recording layer.
Examples of the water-soluble or water-dispersible binder used in the intermediate layer include the substances described in the undercoat layer. Among them, various modified polyvinyl alcohols, cellulose derivatives and casein are preferable, and acetoacetylated polyvinyl alcohols and carboxy-modified polyvinyl alcohols are more preferable.

Further, it is desirable to add a pigment to the coating solution for the intermediate layer in order to enhance the smoothness and to enhance the adhesion with the overcoat layer due to the anchoring effect. Examples of the pigment in this case include calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, inorganic pigments such as colloidal silica, and styrene. Examples thereof include microballs, nylon powder, polyethylene powder, urea-formalin resin filler, and organic pigments such as raw starch granules. The amount used is 5 to 500 parts by weight, preferably 80 to 350 parts by weight, based on 100 parts by weight of the resin component.

Then, in the coating solution for forming the intermediate layer, if necessary, curing of glyoxal, methylolmelamine, potassium persulfate, ammonium persulfate, sodium persulfate, ferric chloride, magnesium chloride, boric acid, ammonium chloride, etc. Agents may be added, if necessary, zinc stearate, calcium stearate, stearic acid amide,
Lubricants such as polyethylene wax, carnauba wax, paraffin wax, and ester wax, surfactants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, sodium salt, alginate, and fatty acid metal salt, benzophenone-based, Various auxiliary agents such as a triazole-based ultraviolet absorber, an antifoaming agent, a fluorescent dye and a coloring dye are appropriately added.

The coating solution for the intermediate layer is prepared as an aqueous coating solution, and if necessary, sufficiently mixed and dispersed by a mixing and stirring pulverizer such as a mixer, an attritor, a ball mill, a roll mill or the like, and then heat-sensitive by various coating devices. It is coated on the recording layer. After coating, it can be cured and dried by irradiating it with ultraviolet rays or electron beams. When using a curing agent together,
The curing agent is not limited to being added to the coating solution for the intermediate layer, and may be applied separately from the coating solution for the intermediate layer. As described above, when separately applied, there is no need to worry about the pot life of the coating liquid, and there is an advantage that a strong curing agent can be selected.

The coating amount of the coating liquid for the intermediate layer is 0.
If it is less than 1 g / m ² , the desired effect of the present invention cannot be sufficiently obtained, and if it exceeds 20 g / m ² , the recording sensitivity of the thermosensitive recording medium may be remarkably lowered, so that the dry weight is not sufficient. It is adjusted in the range of 0.1 to ²⁰ g / m ² , preferably 0.5 to 10 g / m ² .

The heat-sensitive recording material of the present invention can be further improved in storability by providing a coat layer similar to this intermediate layer on the back surface side of the support of the heat-sensitive recording material, if necessary. It is a preferred embodiment that the heat-sensitive recording material of the present invention is processed into an adhesive label by subjecting the back surface to an adhesive treatment. Then, various known techniques in the field of thermal recording material manufacturing can be added as necessary.

In particular, since a recording material having a high recording density and gloss can be obtained by further increasing the smoothness of the surface of the intermediate layer, the Bekk smoothness of the surface of the intermediate layer can be improved by smoothing it with a super calender or the like. It is desirable to adjust it to 100 seconds or longer, more preferably 500 seconds or longer.

In the heat-sensitive recording material of the present invention, an overcoat layer containing an ionizing radiation curable resin is provided on the intermediate layer formed as described above. Examples of the ionizing radiation curable resin forming the overcoat layer include the prepolymers and monomers listed below.

As the prepolymer, (a) aliphatic, alicyclic, poly (meth) acrylate of polyhydric alcohol having 2 to 6 aromatics and polyalkylene glycol; (b) aliphatic, alicyclic, aromatic (A) poly (meth) acrylates of polyhydric alcohols in which alkylene oxide is added to polyhydric alcohols of aromatic or aromatic divalent to hexavalent; (c) poly (meth) acryloyloxyalkyl phosphates; (d) polyester poly (Meth) acrylate; (e) Epoxy poly (meth) acrylate; (f) Polyurethane poly (meth) acrylate; (g) Polyamide poly (meth) acrylate;
(h) Polysiloxane poly (meth) acrylate; (i) Vinyl-based or diene-based low polymer having a (meth) acryloyloxy group at a side chain and / or terminal; (j) The above (a) to
(i) There are modified oligoester (meth) acrylates and the like.

Examples of the monomer include (a) a carboxyl group-containing monomer represented by ethylenically unsaturated mono- or polycarboxylic acid and the like, and a carboxylic acid group-containing unit amount such as an alkali metal salt, ammonium salt or amine salt thereof. (B) ethylenically unsaturated (meth) acrylamide or alkyl-substituted (meth) acrylamide, an amide group-containing monomer represented by vinyl lactams such as N-vinylpyrrolidone;
(c) a sulfonic acid group-containing monomer represented by an aliphatic or aromatic vinyl sulfonic acid and an alkali metal salt thereof,
Sulfonate group-containing monomers such as ammonium salts and amine salts; (d) Hydroxyl group-containing monomers typified by ethylenically unsaturated ethers of polyols and (meth) acrylate esters of polyhydric alcohols; (e) Amino group-containing monomer such as dimethylaminoethyl (meth) acrylate-2-vinylpyridine; (f) Quaternary ammonium salt group-containing monomer;
(g) alkyl ester of ethylenically unsaturated carboxylic acid;
(h) Nitrile group-containing monomer such as (meth) acrylonitrile; (i) Styrene; (j) Vinyl acetate, ester of ethylenically unsaturated alcohol such as (meth) allyl acetate; (k)
Mono (meth) acrylates of alkylene oxide addition polymers of compounds containing active hydrogen; (l) Ester group-containing bifunctional monomer represented by diester of polybasic acid and unsaturated alcohol; (m) Activity Bifunctional monomer comprising diester of alkylene oxide addition polymer of hydrogen-containing compound and (meth) acrylic acid; (n) bisacrylamide such as N, N-methylenebisacrylamide; (o) divinylbenzene, divinyl 2 such as ethylene glycol, divinyl sulfone, divinyl ether, divinyl ketone
Functional monomer; (p) Ester group-containing polyfunctional monomer represented by polyester of polycarboxylic acid and unsaturated alcohol; (q) Alkylene oxide addition polymer of compound containing active hydrogen and (meth) Polyfunctional monomers composed of polyester with acrylic acid; (r) Polyfunctional unsaturated monomers such as trivinylbenzene. The above ionizing radiation curable resins may be used in combination of two or more kinds.

In the present invention, in the coating liquid for the overcoat layer, in addition to the ionizing radiation curable resin, if necessary,
Various inorganic pigments such as calcium carbonate and titanium dioxide, pigments obtained by surface-treating inorganic pigments with organic acids, benzoguanamine resin powders, raw starch granules, organic pigments such as polyolefin microballs, non-electron beam curable resins, defoaming agents, silicone-based and Additives such as a non-silicon type leveling agent, a lubricant, a surfactant, a plasticizer, and an ultraviolet absorber can also be added as appropriate. Examples of the non-electron beam curable resin include acrylic resin, silicon resin, alkyd resin, fluororesin, butyral resin and the like.

By adjusting the kinds and blending ratios of various additives, it is possible to form a heat-sensitive recording material having a wide range of surface properties from matte tone to strong gloss.

The above resin components are mixed in a suitable manner with a mixer or the like.
After thoroughly mixing with a combined stirrer, above the intermediate layer
Can be applied by various known methods.
The viscosity can be adjusted by heating the minutes. Also, apply
The amount is not necessarily limited, but 0.1 g / m²Not yet
At full, the desired effect of the present invention cannot be expected, and 20 g / m ²
If the coating amount exceeds the limit, the recording sensitivity of the obtained recording material
0.1-20g / m as it may decrease², More preferred
1 to 10 g / m²It is desirable to adjust within a range
Yes.

The overcoat layer formed on the intermediate layer is cured by irradiation with ionizing radiation. Examples of the ionizing radiation include electron beams, ultraviolet rays, α rays, β rays, γ rays, and X rays.
Rays, neutron rays, etc., but α rays, β rays, γ rays, X
An electron beam or an ultraviolet ray, which is easy to handle, is preferably used because the ray is dangerous to the human body.

When an electron beam is used, the amount of the electron beam to be irradiated is preferably 0.1 to 15 Mrad, more preferably 0.5 to 10 Mrad. If it is less than 0.1 Mrad, the resin component cannot be sufficiently cured, and excessive electron beam irradiation exceeding 15 Mrad may cause color development or discoloration of the thermosensitive recording medium. May cause a decline. As an electron beam irradiation method, for example, a scanning method, a curtain beam method, a broad beam method or the like can be adopted, and an accelerating voltage for irradiation is 100 to 300 KV.
The degree is appropriate.

On the other hand, when ultraviolet rays are used, it is necessary to mix at least a polymerization initiator or a sensitizer in the coating composition, which is 0.2 to 10% by weight, preferably 0.5. It is added in the range of about 5% by weight. As a light source for UV irradiation, 1 to 50 UV lamps, xenon lamps, tungsten lamps and the like are used, and UV rays having an intensity of about 40 to 200 W / cm are preferably irradiated.

Examples of the polymerization initiator and sensitizer include thioxanthone, benzoin, benzoin alkyl ether xanthone, dimethylxanthone, benzophenone, anthracene, 2,2-diethoxyacetophenone, benzyldimethylketal, benzyldiphenyldisulfide, anthraquinone, 1- Chloroanthraquinone, 2-
Examples thereof include ethylanthraquinone, 2-tert-butylanthraquinone, N, N′-tetraethyl-4,4′-diaminobenzophenone, and 1,1′-dichloroacetophenone.

The electron beam irradiation method is most preferably used because it has higher productivity than the ultraviolet irradiation method, there is no problem of odor and coloring due to addition of a sensitizer, and a uniform crosslinked structure is easily obtained.

The heat-sensitive recording material of the present invention thus obtained can be further smoothed with a super calender or the like to further improve the recording density and the unevenness of the recording density.

In the thermal recording material of the present invention, as described above,
The binder content in the undercoat layer is important. When the binder content in the undercoat layer is high, the barrier property of the undercoat layer is high. The barrier property of the overcoat layer of the ionizing radiation curable resin is extremely high. In this way, when there are high barrier layers above and below the heat-sensitive recording layer, printing blisters occur due to expansion when the heat-sensitive recording layer melts due to heating of the heat-sensitive printing. This is a phenomenon that is more often observed as the sensitivity of the thermal recording layer is higher. The thermal recording material of the present invention can improve the printing blister by adjusting the binder content in the undercoat layer.

[0047]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively.

Example 1 Formation of Undercoat Layer As the coating solution for the undercoat layer, 75 parts of calcined kaolin, 13 parts of calcium carbonate, 6 parts of styrene-butadiene copolymer emulsion (solid content), 6 parts of oxidized starch, and 150 parts of water were prepared. Then, a base paper of 55 g / m ² was used as a base paper, and the base paper was coated and dried with a pure blade coating so that the coating amount after drying was 8 g / m ² to obtain a heat-sensitive base paper having an undercoat layer. . Formation of thermosensitive recording layer Liquid A preparation 10 parts of 3-dibutylamino-7- (o-chlorophenylamino) fluorane, 5% aqueous solution of methylcellulose 5
Parts of water and 30 parts of water, the average particle size is 3μ in a sand mill.
It was crushed until it reached m. Liquid B preparation 4-hydroxy-4'-isopropoxydiphenyl sulfone 20 parts, methyl cellulose 5% aqueous solution 5 parts, water 55 parts,
The composition was pulverized with a sand mill until the average particle diameter became 3 μm. As a coating solution for the heat-sensitive recording layer, 45 parts of solution A, solution B
80 parts, 50 parts of 20% oxidized starch aqueous solution, and 10 parts of water were mixed and stirred to prepare heat-sensitive base paper having the above-mentioned undercoat layer so that the coating amount after drying was 6 g / m ² I got a record. Formation of intermediate layer As an intermediate layer coating solution, 8 parts of acetoacetylated polyvinyl alcohol (trade name: Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)
% Aqueous solution 1000 parts, calcium carbonate (trade name: Softon 18
00, made by Bihoku Kouka Co., Ltd.) and 100 parts of water were prepared, and the coating amount after drying was 4 g / m ² on the recording layer of the above-mentioned thermal recording material.
Was coated and dried to obtain a thermosensitive recording medium having an intermediate layer having a Beck's smoothness of 800 seconds. Formation of overcoat layer As an overcoat layer coating liquid, an acrylate prepolymer (trade name: EBX135, manufactured by Toagosei Kagaku Co., Ltd.) 100
Part and a silicone surfactant of 0.1 part were prepared and applied onto the above-mentioned intermediate layer so that the dry coating amount was 3 g / m ^2, and the electron curtain type electron beam irradiation device (CB:
A thermosensitive recording medium having an overcoat layer was obtained by curing the resin component by treating it with an irradiation dose of 3 Mrad (150 type, manufactured by ESI).

Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was formed with the following composition. 70 parts of calcined kaolin,
12 parts of calcium carbonate, 9 parts of styrene-butadiene copolymer emulsion (solid content), 9 parts of oxidized starch, 150 parts of water.

Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that the undercoat layer was formed with the following composition. 80 parts of calcined kaolin,
14 parts of calcium carbonate, 3 parts of styrene-butadiene copolymer emulsion (solid content), 3 parts of oxidized starch, 150 parts of water.

Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was formed with the following composition. Calcined kaolin 83.5
Parts, calcium carbonate 14.5 parts, styrene-butadiene copolymer emulsion (solid content) 1 part, oxidized starch 1 part, water 1
50 copies

Example 5 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the coating amount of the undercoat layer was 16 g / m ² .

Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was coated and dried with a bar coater.

Comparative Example 1 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was formed with the following composition. 64 parts of calcined kaolin,
Calcium carbonate 11 parts, styrene-butadiene copolymer emulsion (solid content) 14.6 parts, oxidized starch 10.4 parts, water 150
Department.

Comparative Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was not provided.

Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the overcoat layer was not provided on the intermediate layer.

The following quality tests were conducted on each of the obtained thermosensitive recording media, and the results are shown in Table 1. (1) Initial printing color density Each thermal recording medium was tested with a thermal inclination tester (manufactured by Toyo Seiki: Condition 120).
Image recording is carried out at ² ° C, 2 kg / cm ² , 10 seconds).
The maximum color density of the obtained recorded image was measured with a Macbeth densitometer (RD-100R type, manufactured by Macbeth Co.). (2) Glossiness The glossiness of the surface of each thermosensitive recording medium is measured by a goniophotometer (MURAKA).
MI COLOR RAB. Made, Glossmeter GM
-3D) at an incident angle of 75 degrees. (The larger the value, the higher the gloss.) (3) Recording suitability Each thermosensitive recording medium is fully automatic labeler (trade name: DP 82
0, manufactured by Ishida Koki Co., Ltd.), and the recording suitability was evaluated according to the following evaluation criteria. A: Recording is possible without any problem. ◯: Printing blister tends to occur, but recording is possible without problems. X: Many printing blisters occur in the printing portion, which causes printing failure. (4) Plasticizer resistance test A vinyl chloride wrap film (manufactured by Mitsui Toatsu Kagaku Co., Ltd.) was wound on a polypropylene pipe (40 mm diameter pipe) in three layers,
A thermosensitive recording material that was printed with a thermal gradient tester was sandwiched on top of it so that the printed surface was on the outside, and a vinyl chloride wrap film was wrapped around it five times. The printing density after 100 hours was Macbeth. It was measured with a densitometer and the maintenance rate of the concentration was calculated. (The larger the value, the better the plastic resistance.)

[0058]

[Table 1]

[0059]

As is clear from the results shown in Table 1, the thermosensitive recording medium of the present invention has a high recording density, high gloss and excellent storability, and has no printing blister trouble when used in a full-auto labeler. The thermosensitive recording medium was excellent in recording suitability.

Claims (3)

[Claims] 1. A pigment and a content of 1 to 20% by weight on a base paper.
An undercoat layer containing an aqueous binder as a main component, a heat-sensitive recording layer containing a color former and a color former that develops a color when contacted with the color former, an intermediate layer containing an aqueous binder, and an overcoat containing an ionizing radiation curable resin. A heat-sensitive recording material, characterized in that a coating layer is sequentially provided and irradiated with ionizing radiation. 2. The thermal recording material according to claim 1, wherein the binder content in the undercoat layer is 5 to 20% by weight. 3. The thermosensitive recording medium according to claim 1, wherein the ionizing radiation is an electron beam.